ω-Alkoxy derivatives of lactams and process for their manufacture

ABSTRACT

Compounds of the formula ##STR1## in which R 4  represents an alkyl radical having from 1 to 4 carbon atoms, 
     R 5  represents a linear or branched alkylene radical having from 1 to 10 carbon atoms in the chain which may be substituted by groups which are not reactive under the applied conditions, and R 6  represents hydrogen or a branched alkyl radical having from 3 to 10 carbon atoms with a secondary or tertiary N-α-C atom, are prepared by anodic alkoxylation of lactams of the formula ##STR2## with an alcohol of the formula R 4  OH, in which formulae R 4 , R 5  and R 6  have the aforesaid meaning, in the presence of at least one alkali metal or tetraalkylammonium tetrafluoroborate, hexafluoroborate or nitrate as conducting salt, at a temperature of up to about 100° C. in an electrolytic cell with stationary or flowing electrolyte. Some of the products are novel. They can be used as intermediates for the manufacture of pharmaceuticals, antistatic agents in textile industries and as intermediates for polymerization reactions and for the preparation of α-amino-α,ω-dicarboxylic acids.

This is a division, of application Ser. No. 751,335 filed Dec. 16, 1976now abandoned.

This invention relates to ω-alkoxy derivatives of lactams and to aprocess for their manufacture.

It has been proposed to react, by an electrochemical process, carboxylicacid amides alkylated on the nitrogen atom of the formula ##STR3## inwhich R¹, R² and R³ represent hydrogen or organic radicals and R¹ and R²may also be linked with each other, with alcohols to obtain thecorresponding N-α-alkoxyalkyl carboxylic acid amides (GermanOffenlegungsschrift 2,113,338). In this process the N-alkyl-carboxylicacid amides are electrolyzed in an excess of an alcohol in the presenceof a conducting salt, for example an alkali metal or a tetraalkylammonium tetrafluoroborate, hexafluorophosphate or nitrate, at atemperature of up to about 100° C. The electrolytic cell may contain astationary or a flowing electrolyte and the amount of current used doesnot exceed 2.4 Faradays per mol of carboxylic acid amide.

It has also been proposed (Belgian Pat. No. 837,906) to electrolyzestarting products specifically mentioned in the DOS 2,113,338, i.e.N-alkylcarboxylic acid amides of the formula ##STR4## in which R¹ hasthe aforesaid meaning, in the presence of very specific conducting saltsto obtain the corresponding N-α-alkoxyalkyl carboxylic acid amides. Inthis process higher amounts of current can be used and, hence, thesubstance yield is improved and, moreover, the reaction mixture can beworked up more easily.

In the aforesaid processes the starting materials used are exclusivelyN-alkylcarboxylic acids which carry 2 hydrogen atoms in at least oneN-alkyl group in α-position to the nitrogen and carry also the group CH₂-R³ on the nitrogen, especially when R¹ and R² are linked with eachother.

Still further, it has been proposed to alkoxylize at the anodesubstantially in the same manner those N-alkylcarboxylic acid amideswhich carry on the nitrogen atom two alkyl groups linked with each other(cf. German Offenlegungsschrift 2,539,777). In the latter process thestarting compounds have the formula ##STR5## in which R¹ has theaforesaid meaning and R^(2') represents a linear or branched alkyleneradical having from 1 to 4 carbon atoms in the chain. Depending on thecurrent amount used, the alkoxylation is effected on one or on both ofthe CH₂ groups linked to the nitrogen atom.

In the anodic alkoxylation of the N-alkylcarboxylic acid amides usedaccording to the process of DOS 2,113,338 it is practically always theCH₂ group of the CH₂ -R³ substituent which is alkoxylated even if theradicals R¹ and R² are linked with each other, i.e. lactams substitutedat the nitrogen atom by the group CH₂ -R³. Products alkoxylated on thenucleus, that is to say in the lactam ring, are practically not formed.

There are known purely chemical reactions to prepare lactams whichadditionally carry an alkoxy group on the carbon atom adjacent to thenitrogen atom (opposite to the carbonyl group). Compounds of this typecan also be considered N,O-acetals. A chemical method to prepare thesecompounds is described, for example, in Liebigs Ann. Chem. 1974, pages539-560, according to which the four-membered ring compounds areprepared, in principle, by the following reaction equation: ##STR6## inwhich R and R' represent organic radicals.

A generalization of this method for the preparation of N,O-acetals withhigher rings has not yet become known.

In view of the fact that N,O-acetals of this type are importantintermediates it is desirable to develop a process permitting thepreparation of such compounds in a simple and uncomplicated mannerindependent of the size of the lactam ring.

This problem could be solved by further developing the alkoxylationreaction described in German Offenlegungsschrift No. 2,113,338 and inBelgian Pat. No. 837,906.

It is therefore the object of the present invention to use as startingmaterials for the electrolysis lactams of the formula ##STR7## in whichR⁵ represents a linear or branched alkylene radical having from 1 to 10carbon atoms in the chain which may be substituted by groups which arenot reactive under the applied conditions, for example hydroxyl orhalogen, preferred substituents of R⁵ being CH₂ OH--, --CH₂ --A--CH₂ CH₂CH₂ --COOR⁷ in which A represents --C.tbd.C--, --CH═CH-- or --CH₂ --CH₂-- and R⁷ stands for hydrogen or a low molecular weight aliphatic (C₁-C₄), cycloaliphatic (C₅ -C₆) or araliphatic (C₆ -C₈) hydrocarbonradical,

R⁶ represents hydrogen or a branched alkyl radical preferably havingfrom 3 to 10 carbon atoms with a secondary or tertiary N-α-C atom whichis difficult to alkoxylate.

The present invention provides a process for the anodic alkoxylation ofN-alkylcarboxylic acid amides with an alcohol of the formula R⁴ OH inwhich R⁴ represents an alkyl radical having from 1 to 4 carbon atoms, inthe presence of at least one alkali metal or tetraalkylammoniumtetrafluoroborate, hexafluorophosphate or nitrate as conducting salt, ata temperature of up to about 100° C. in an electrolytic cell withstationary or flowing electrolyte, which comprises using as N-alkylcarboxylic acid amide a lactam of the formula ##STR8## in which R⁵ andR⁶ have the aforesaid meaning. The reaction yields lactams alkoxylatedin the nucleus and having the following formula ##STR9##

Suitable starting compounds in the process of the invention are, forexample, azetidinone-2, 3-methyl-azetidinone-2,1-isopropylpyrrolidone-2, 1-isopropyl-4-hydroxymethyl-pyrrolidone-2,1-isopropyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethylpyrrolidone-2,1-tert.-butylpyrrolidone-2, piperidone-2, ε-caprolactam, the lactams ofω-amino-caprylic acid, capric acid, lauric acid, preferably, however,1-isopropyl-4-hydroxymethylpyrrolidone-2, compounds of the formula##STR10## in which R⁷ represents a C₁ -C₄ alkyl radical, a C₅ -C₆cycloalkyl radical or an araliphatic radical, and more preferably1-isopropyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethyl-pyrrolidone-2,(in which A is --C.tbd.C--, R⁶ is ##STR11## which compounds can beprepared as described in German Offenlegungsschriften Nos. 2,452,536 and2,528,036 according to the following reaction scheme: ##STR12##

In the case of A being --C.tbd.C-- the final compound can be partiallyhydrogenated to form the --CH═CH-- group or completely hydrogenated to--CH₂ --CH₂ -- by a method known per se.

With the use of the preferred starting compounds the following finalcompounds are obtained: ##STR13##

Products of this type are novel. The latter two compounds can be used asintermediates for the manufacture of pharmaceuticals, especially thosehaving prostaglandine-like effects (cf. Application Ser. No. 751,165,filed Dec. 16, 1976, now U.S. Pat. No. 4,096,274 filed concurrentlyherewith).

A pharmaceutical of this type is, for example, the compound of theformula ##STR14## obtained by oxidation of the CH₂ OH group in thelatter compound to the CHO group, reaction with ##STR15## in which eachR stands for an alkyl radical and the radical R bound to the ##STR16##may also represent an optionally substituted phenoxy or cycloalkylradical, and hydrogenation of the azetocarbonyl group.

Further preferred starting compounds in the process of the invention arelactams with 5 to 13 ring members of the formula ##STR17## in which R⁵represents --(CH₂)₂₋₁₀, preferably --(CH₂)₃ --, --(CH₂)₄ -- and--(CH₂)₁₀ --,

R⁶ stands for hydrogen or a branched alkyl radical having from 3 to 10carbon atoms with a secondary or tertiary N-α-C atom, preferablyhydrogen.

The compounds obtained in this manner are also novel, they have theformula ##STR18## in which R⁵ and R⁶ have the aforesaid meaning, R⁴represents an alkyl radical with 1 to 4 carbon atoms preferably CH₃.Compounds of this type can be used as antistatic agents in textileindustries and as intermediates in polymerization reactions and in thepreparation of α-amino-α, ω-dicarboxylic acids according to thefollowing reaction scheme: ##STR19##

Suitable alcohols R⁴ OH to carry out the process of the invention aremethanol, ethanol, n-propanol, isopropanol, n-butanol, sec.-butanol,preferably, however, methanol and ethanol and more preferably methanol.

The conducting salt to be used in the process of the invention arealkali metal salts (Li, Na, K, Rb, Cs) and tetraalkyl ammonium salts oftetrafluoroboric acid, hexafluorophosphoric acid and nitric acid. Theyare used either singly or in admixture with one another. The alkylradicals in the tetraalkyl ammonium group have 1 to 6 and preferably 1to 4 carbon atoms, especially the methyl and ethyl radical. Thefollowing conducting salts are mentioned by way of example:Na-tetrafluoroborate, Na-nitrate, K-tetrafluoroborate,K-hexafluorophosphate, Rb-nitrate, tetramethylammoniumtetrafluoroborate, tetraethylammonium tetrafluoroborate,tetra-n-butylammonium tetrafluoroborate, tetraethylammoniumhexafluorophosphate, tetra-n-propylammonium hexafluorophosphatetetra-n-butylammonium hexafluorophosphate, or tetramethylammoniumnitrate. Preferred conducting salts are the alkali metal and tetraalkylammonium tetrafluoroborates especially NaBF₄, KBF₄ and (CH₃)₄ -NBF₄.

The concentration of conducting salt in the electrolysis solution shouldbe in the range of from about 0.01 to about 2.0 mol/l, preferably about0.02 to 1.0 mol/l. The temperature of the electrolysis solution shouldbe in the range of from about -10° to +100° C., preferably about 0° to60° C.

In the electrolytic solution the molar proportion of starting acid amideto alcohol is in the range of from about 1:1 to about 1:100, preferably1:2 to 1:60 and more preferably 1:5 to 1:50.

The electrochemical alkoxylation according to the invention may becarried out discontinuously or continuously.

The process will now be described in further detail by way of exampleonly, with reference to the accompanying drawing which is a view, partlyin section, of an electrolysis cell suitable for carrying out theprocess of the invention in discontinuous manner.

Referring to the drawing, an electrolytic cell (1) is equipped with atightly sealing cover or lid (2), through which the power supply linesfor electrodes (3) and (4) are led and in which an opening (5) for thesupply of the electrolysis solution, an opening (6) for the discharge ofgas and a thermometer (9) are fitted. The orifice (6) for the dischargeof gas may be equipped with a reflux condenser, in which evaporatingportions of the electrolysis mixture may be recovered by condensation.The electrolytic cell (1) is encased and may be connected to a heatingor cooling liquid circuit by means of inlet and outlet sockets (7 and8). The temperature of the electrolysis solution is controlled by thethermometer (9) or a thermosensor. The two electrodes (3) (anode) and(4) (cathode) are set up at a distance of from 0.5 to 50 mm, preferablyfrom 1 to 15 mm.

As electrodes there are used nets or sheets of palladium or platinum ornoble metal-coated metal electrodes, preferably titanium electrodes,mixed oxide-coated metal electrodes (as anodes), preferably titaniumanodes, or graphite plates provided with slits or not. The use ofelectrode nets is especially advantageous, because these facilitate thedischarge of the gaseous hydrogen formed during the electrolysis, andthe uniform and thorough mixture of the electrolysis solution isadditionally favoured by the gas current formed. The verticaldisposition of the electrodes may be replaced, if desired, by ahorizontal one. It is also possible to use several electrode pairs; ablock-like combination of angular or non-angular capillary splitelectrodes, optional with vibration of the electrodes, has provedespecially efficient. The solution is mixed vigorously duringelectrolysis by means of an agitator, for example a magnetic stirrer(10) or by circulation by pumping, especially in case of the block-likecombinations.

If the process is carried out continuously, an additional orifice may beset in the cover (2) of the electrolysis vessel (1) for pump-circulatingthe electrolysis solution continuously. A portion of the electrolysissolution which is circulated by pumping is separated for work up of theproduct. After determination of the ratio of the desired reactionproduct to the starting material in the electrolysis solution by thenuclear magnetic resonance spectrum or by gas chromatography, thesolution is worked up in known manner. The starting materials, recoveredupon distillation, may be adjusted to the molar ratio employed and thenmetered into the continuously recirculating electrolysis solutiontogether with the required quantity of the conducting salt or salts.

The electrolysis may be carried out under normal pressure, but may beperformed under reduced pressure. So as to avoid the formation ofexplosive gas mixtures of hydrogen and air, the addition of an inertgas, e.g. nitrogen, is advantageous.

The conducting salt is suitably added after having prepared thealcoholic solution. However, this order may be changed.

There is no need to exclude water strictly from the electrolyte sinceminor amounts thereof do not affect the course of reaction.

The process gives an especially high yield and is especially efficientwith respect to energy consumed, if the conversion of cyclic carboxylicacid amide is increased, e.g. to more than 99%, this step being alsoadvantageous for a better work up of the electrolysis solution.Therefore, the electrolysis is advantageously continued untilpractically the total starting material is converted so that there is noneed later to separate this from the the reaction product.

The electrolysis current is switched off after having led through thequantity of electricity desired, and the electrolysis discharge is thenfreed from the conducting salt and worked up in known manner, preferablyby distillation. The degree of purity of the product may be determinedby a nuclear magnetic resonance spectrum.

The current density is chosen in the range of from about 1 to 50 A/dm²,preferably 2 to 30 A/dm². Lower current densities are also possible,though they diminish the rate at which the product is formed. Thequantity of electricity should be about 2 to 4, preferably 2 to 3.5 andespecially 2 to 3 Faradays/mol of starting lactam.

The α-alkoxy derivatives of cyclic carboxylic acid amides preparedaccording to the electrochemical process of the invention are valuableintermediate products, especially for the manufacture ofpharmaceuticals, having, in the first place, prostaglandine like effectsand also luteolytic, bronchospasmolytic and/or antihypertensiveproperties and properties to inhibit the secretion of gastric juice.

The following examples illustrate the invention.

EXAMPLE 1

17.6 g of azetidinone-2- and 39.6 g of methanol are electrolyzed in anelectrolytic cell having a capacity of approximately 60 ml in thepresence of 0.82 g of tetra-m-propylammonium hexafluorophosphate asconducting salt. As electrodes two concentrically placed platinum netcylinders having 225 meshes per cm² and diameters of 15 and 30 mm,respectively, and a height of 50 mm are immersed in the solution, theouter electrode being connected as anode. During electrolysis thetemperature is maintained at about 10° C. After having switched on theelectrolysis direct current, the current density at the anode is 1A/dm². The current is switched off after passage of 2.5 Faradays per molof azetidinone-2. The calculated average cell tension is 29.6 volts.After working up by molecular distillation there are obtained 12.7 g of4-methoxy-azetidinone-2 (boiling point 41° C. under 0.013 millibar,melting point 62°-63° C.), corresponding to a material yield of 50.9%and a current efficiency of 40.7%.

EXAMPLE 2

In an electrolytic cell as described in Example 1 21.0 g ofpyrrolidone-2 and 39.6 g of methanol are electrolyzed in the presence of0.40 g of tetramethylammonium tetrafluoroborate as conducting salt.After having switched on the electrolysis direct current, the density atthe anode is 3 A/dm². The current is switched off after the passage of2.0 Faradays per mol of pyrrolidone-2. The calculated average celltension is 35.2 volts. After working up by molecular distillation, 14.3g of 5-methoxypyrrolidone-2 are obtained (boiling point 87°-90° C. under0.14 millibar, melting point 56°-58° C.), corresponding to a materialyield and a current efficiency of 50.1% each.

EXAMPLE 3

In an electrolytic cell as described in Example 1 14.7 g ofpyrrolidone-2 and 39.5 g of ethanol are electrolyzed in the presence of0.28 g of tetramethyl ammonium tetrafluoroborate as conducting salt.After having switched on the electrolysis direct current, the anodecurrent density is 3 A/dm². After having passed 2.0 Faradays per mol ofpyrrolidone-2 the current is switched off. The calculated average celltension is 48.2 volts.

Working up by molecular distillation yields 12.0 g of5-ethoxypyrrolidone-2 (melting point 54°-56° C.), corresponding to amaterial yield and a current efficiency of 54.2% each.

EXAMPLE 4

In an electrolytic cell as described in Example 1 10.0 of1-isopropyl-4-hydroxymethylpyrrolidone and 54.6 g of methanol areelectrolyzed in the presence of 0.34 g of tetramethylammoniumtetrafluoroborate as conducting salt. After having switched on theelectrolysis direct current, the anode current density is 2 A/dm². Afterthe passage of 2.2 Faradays per mol of1-isopropyl-4-hydroxymethylpyrrolidone, the current is switched off. Thecalculated average cell tension is 48.5 volts.

After separation of the methanol and separation by column chromatography(silica gel/chloroform + ethanol [9:1])

9.0 g of 1-isopropyl-4-hydroxymethyl-5-methoxypyrrolidone-2 areobtained, corresponding to a material yield of 75.6% and a currentefficiency of 68.7%. NMR characteristics of the compound: NMR 100millicyles per second; solvent: ##STR20##

EXAMPLE 5 (a) Preparation of 1-methyl- and1-isopropyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethyl-pyrrolidone1-methyl compound

(α) 29.4 g (138 mols) of1-methyl-4-(2-tetrahydropyranylhydroxymethyl)-pyrrolidone dissolved in90 ml of diethyl ether are added over a period of 20 minutes whilestirring at -70° C. to 150 mols of LiN(i-C₃ H₇)₂ in 150 ml of diethylether. Stirring is continued for 45 minutes whereupon the solution istransferred to a coolable dropping funnel (-35° to -40° C.) and added,while stirring over a period of 60 minutes, to a solution cooled to -70°C. of 29.1 g (149 mols) of 1-bromo-6-chloro-hexine(2) in 135 ml ofether. Stirring is continued for another 90 minutes, the mixture isslowly heated to room temperature, 75 ml of water are added dropwise,the organic phase is separated and the aqueous phase is extracted threetimes, each time with 50 ml of diethyl ether. The combined ether phasesare washed three times with 40 ml each of cold sulfuric acid and oncewith 50 ml of water. After drying and concentrating under reducedpressure the organic phase, 46.6 g of crude1-methyl-3-[6-chloro-2-hexine-yl(1)]-4-(2-tetrahydropyranyl-hydroxymethyl)pyrrolidone (R_(F) 0.42 (ethyl acetate)) are obtained The compound isused for the following reaction stage without further purification.

(β) 7.5 g (153 mols) of sodium cyanide are dissolved in 90 ml ofdimethyl sulfoxide and the solution is heated to 80° C. 46.6 g (142.5mmols) of crude1-methyl-3-[6-chloro-2-hexine-yl(1)]-4-(2-tetrahydropyranyl-hydroxymethyl)-pyrrolidonedissolved in 40 ml dimethyl sulfoxide are then added dropwise whilestirring and the mixture is stirred for 3 to 6 hours at 80° C. Thecourse of the reaction is followed by thin layer chromatography (ethylacetate). When the reaction is terminated, the mixture is cooled to 10°C., 200 ml of water are added and the mixture is extracted three times,each time with 200 ml of diethyl ether. The combined ether phases arewashed three times with saturated sodium chloride solution and dried.After concentration under reduced pressure 43.7 g of crude1-methyl-3-[6-cyano-2-hexine-yl(1)]-4-(2-tetrahydropyranyl-hydroxymethyl)-pyrrolidone[R_(F) 0.39 (ethyl acetate)] are obtained, which is used for the nextreaction without further purification.

(γ) 11 g (0.275 mol) of sodium hydroxide are dissolved in 33 ml ofwater, 43.7 g (137.5 mols) of1-methyl-3-[6-cyano-2-hexine-yl(1)]-4-(2-tetrahydropyranyl-hydroxymethyl)-pyrrolidonedissolved in 135 ml of ethyl alcohol are added and the whole is refluxedfor 18 hours. The alcohol is removed under reduced pressure, 150 ml oficecold 2N sulfuric acid are added to the residue while cooling with iceand the whole is extracted ten times, each time with 100 ml of diethylether. After drying and concentrating the combined ether phases, 47.4 gof crude1-methyl-3-[6-carbohydroxy-2-hexine-yl)]-4-(2-tetrahydropyranyl-hydroxymethyl)-pyrrolidoneare obtained which is directly taken up in 250 ml of methylene chlorideand to which 380 ml of a 0.5 molar ethereal diazomethane solution areadded at 0° C. The mixture is allowed to stand for 30 minutes at 0° C.and for 1 hour at room temperature. After concentration under reducedpressure, 43.7 g of crude1-methyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-(2-tetrahydropyranyl-hydroxymethyl)-pyrrolidone[R_(F) 0.45 (ethyl acetate)] are obtained.

(δ) The product obtained is dissolved in 200 ml of methanol, 3 drops ofconcentrated hydrochloric acid are added and the mixture is refluxed for75 minutes. After concentrating under reduced pressure, the remainingoil is purified by column chromatography (silica gel/ethyl acetate) toremove by-products, then ethyl acetate:ethanol 10:1.5). 25 g of1-methyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethyl-pyrrolidone[R_(F) 0.14 (ethyl acetate)] are obtained.

n_(D) ²⁰ = 1.5005 IR(CH₂ Cl₂): = 3450 (OH), 1740 (C=O), 1690 (C=O) cm⁻¹NMR:solvent: CDCl₃ :N-CH₃ : 2.82 ppm; O-CH₃ : 3.64 ppm.

1-ISOPROPYL COMPOUND

This compound is prepared in analogous manner using as starting compound1-isopropyl-4-(tetrahydropyranyl-hydroxymethyl)-pyrrolidone. n_(D) ²⁰ =1.4945 ##STR21##

(b) ANODIC OXIDATION OF THE 1-ISOPROPYL COMPOUND

In an electrolytic cell having a capacity of about 60 ml 5.0 g of1-isopropyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethylpyrrolidone-2and 57.7 g of methanol are electrolyzed in the presence of 0.09 g oftetramethylammonium tetrafluoroborate as conducting salt. As electrodestwo concentrically diposed platinum net cylinders having 225 meshes percm² and diameters of 15 and 30 mm, respectively, and a height of 50 mmare immersed in the solution. The outer electrode is connected as anode.During electrolysis the temperature is maintained at about 10° C. Afterhaving switched on the electrolysis direct current, the anode currentdensity is found to be 1 A/dm². After having passed 2.44 Faradays permol of starting lactam the current is switched off. The calculatedaverage cell tension is 31.2 volts.

After separation of the methanol by distillation under reduced pressurethere are obtained by column chromatography (silica gel/ethyl acetate)3.35 g of1-isopropyl-3-[carbomethoxy-2-hexine-yl(1)]-4-hydroxymethyl-5-methoxypyrrolidone-2(R_(F).sbsp.1 0.61; R_(F).sbsp.2 0.55 (ethyl acetate), corresponding toa material yield of 60.8% and to a current efficiency of 50.1% of thetheory.

EXAMPLE 6

In an electrolytic cell as described in Example 1, but having a capacityof 400 ml 87.3 g of caprolactam and 247.1 g of methanol are electrolyzedin the presence of 1.24 g of tetramethylammonium tetrafluoroborate asconducting salt. The platinum net cylinders have a height of 100 mm.After having switched on the electrolysis direct current, the anodecurrent density is found to be 3 A/dm². After having passed 3.0 Faradaysper mole of ε-caprolactam, the current is switched off. The calculatedaverage cell tension is 26.8 volts.

After working up by molecular distillation, 61.1 g ofε-methoxy-caprolactam (boiling point 106°-108° C. under 0.6 millibar;melting point 65°-66° C.) are obtained, corresponding to a materialyield of 55.3% and a current efficiency of 36.9%.

EXAMPLE 7

In an electrolytic cell as described in Example 6 87.3 g of caprolactamand 247.1 g of methanol are electrolyzed in the presence of 9.7 g ofpotassium tetrafluoroborate as conducting salt. After having switched onthe electrolysis direct current, the anode current density is 1 A/dm².The current is switched off after passage of 3.0 Faradays per mol ofε-caprolactam. The calculated average cell tension is 30.3 volts.

After working up by molecular distillation, 59.0 g ofε-methoxy-caprolactam (boiling point 106°-108° C. under 0.6 millibar;melting point 65°-66° C.) are obtained, corresponding to a materialyield of 53.4% and a current efficiency of 35.6%.

EXAMPLE 8

In an electrolytic cell as described in Example 6 78.6 g of piperidone-2and 253.9 g of methanol are electrolyzed in the presence of 1.28 g oftetramethylammonium tetrafluoroborate as conducting salt. After havingswitched on the electrolysis direct current, the anode current densityis found to be 2 A/dm². After passage of 2.4 Faradays per mol ofpiperidone-2, the current is switched off. The calculated average celltension is 12.4 volts.

After removal of the methanol and twofold recrystallization indi-isopropyl ether, 73.4 g of 6-methoxypiperidone-2 (melting point110°-111° C.) are obtained, corresponding to a material yield of 71.1%and a current efficiency of 59.2%.

EXAMPLE 9

In an electrolytic cell as described in Example 6 87.3 g ofε-caprolactam and 247.1 g of methanol are electrolyzed in the presenceof 8.4 g of sodium tetrafluoroborate as conducting salt. After havingswitched on the electrolysis direct current, the anode current densityis found to be 3 A/dm². After passage of 3.0 Faradays per mol ofε-caprolactam the current is disconnected. The average cell tension iscalculated to be 12.9 volts. After working up by molecular distillation,80.0 g of ε-methoxy-ε-caprolactam are obtained, corresponding to amaterial yield of 72.4% and a current efficiency of 48.3%.

EXAMPLE 10

A test is carried out under the conditions of Example 9 with theexception, however, that a mixture of 4.2 g of sodium tetrafluoroborateand 5.9 g of tetramethylammonium tetrafluoroborate is used as conductingsalt. After disconnection of the current, the average cell tension iscalculated to be 18.7 volts. By working up by molecular distillation78.4 g of ε-methoxy-ε-caprolactam are obtained, corresponding to amaterial yield of 71.0% and to a current efficiency of 47.3%.

EXAMPLE 11

In an electrolytic cell as described in Example 6 72.24 g oflaurinolactam and 293.33 g of methanol are electrolyzed in the presenceof 0.6 g of tetramethylammonium tetrafluoroborate as conducting salt.After having switched on the electrolysis direct current, the anodecurrent density is found to be 2 A/dm². After having passed 3.5 Faradaysper mol of laurinolactam, the current is disconnected. The calculatedaverage cell tension is 48.1 volts.

After working up and recrystallization 42.4 g of ω-methoxylaurinolactamof the formula ##STR22## (melting point 153.5°-154.5° C.) are obtained,corresponding to a material yield of 50.9% and a current efficiency of29.1%.

EXAMPLE 12

In an electrolytic cell as described in Example 1 16.7 g of caprolactamand 75.8 g of methanol are electrolyzed in the presence of 0.19 g oftetramethylammonium tetrafluoroborate as conducting salt. After havingswitched on the electrolysis direct current, the anode current densityis 1 A/dm². The current is disconnected after having passed 3.0 Faradaysper mol of caprylolactam. The calculated average cell tension is 35.2volts.

After working up by molecular distillation 11.6 g ofω-methoxycaprylolactam of the formula ##STR23## are obtained,corresponding to a material yield of 57.2% and a current efficiency of38.3%.

What is claimed is:
 1. A compound of the formula ##STR24## in which Arepresents --CH.tbd.C--, --CH═CH-- or --CH--CH--R⁴ represents an alkylgroup having from 1 to 4 carbon atoms, R⁶ represents hydrogen or abranched alkyl group having from 3 to 10 carbon atoms with a secondaryor tertiary N-α-C atom, and R⁷ represents an alkyl group having from 1to 4 carbon atoms, a cycloalkyl group having 5 or 6 carbon atoms or ancarbocyclic aralkyl group of 6 to 9 carbon atoms.
 2. A compound asclaimed in claim 1 in which A stands for --C.tbd.C--, R⁴ and R⁷ standfor CH₃ and R⁶ stands for ##STR25## 3.1-methyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethyl-5-methoxy-pyrrolidone.4.1-isopropyl-3-[6-carbomethoxy-2-hexine-yl(1)]-4-hydroxymethyl-5-methoxy-pyrrolidone.